1. Field of the Invention
This invention relates to road-transportable drill rigs for drilling boreholes into the earth to extract hydrocarbons, such as oil and natural gas, as well as other minerals.
2. Description of the Related Art
Drilling masts are the vertical structures used to support the drill string while a well is being drilled. Masts are usually rectangular in shape as opposed to the generally pyramidal shape of a derrick. The rectangular shape offers very good stiffness that allows the mast to be moved to a horizontal position for transport. Thus, drilling masts are very common on portable land rigs.
FIG. 1A shows a mast assembly 120 for a transportable (i.e. portable) drill rig 100 of the prior art, but which has many components in common with the present invention. The mast assembly 120 has a derrick 112, an A-frame 114, as part of the rig structure 120, on a rig floor 116 mounted to a substructure 118. The mast 120 is pivotally connected to the floor 116. The mast 120 is a typical drilling rig mast with top sheaves (not shown). The rig floor of this prior art drill rig is supported upon a base 122 with conventional cross-bracing members 118, 118a, and 118b which brace the rig during operation. Typical components of these rigs 100 also include drawworks 130, a control system 134 and other machinery well known and commonly used in the industry.
The rigs also typically have a number of structural members (140A, 140B & 140C) that carry the load of the rig 100 as it stands upright. However, since these rigs are portable, they are made to be collapsible during transport, and are therefore typically raised from a stacked/collapsed position with a wire rope system using the existing drawworks 130 system of the rig through a series of pulleys, or by hydraulic cylinders. Very high tension loads are applied to the wire rope during assembly, and a relatively complex series of pulleys, etc. may be required to raise the rig floor. It would be preferable to utilize a more easily controlled lifting system that did not require a cabling system carrying high tensile loads to raise these rig floors.